There are two ends to this answer. On the one hand you don't want to smother her and on the other you don't want to seem disinterested. It is true that all women are different, but somethings remain fairly constant. So, (for women you've only known a short time, and not in the first conversation) you want to calmly, casually let her know that you're interested, a compliment or suggestive hypothetical, (CLEAN, like "If I took you out to dinner...") something that tells her where you'd like the relationship to go. Gauge her reaction. This is important, she will have two reactions, initial and thought out. If her initial reaction is awful, you have your answer without the awkwardness of rejection. If her reaction is tempered give her time to think about it before you bring it up again; at which point you can again test her reaction subtly, or just go for it. If her reaction is positive ask her at the end of the conversation.
Or if your comfortable and calm, just walk up, introduce yourself and ask her out. It's really a lot easier than it sounds, but you do have to be relaxed or you'll just come off as creepy. Oh, and start with something small (coffee) and specific (Thursday at Denny's, if she says she's busy, ask her when she's free).
Signed,
A man whose had real relationships